Conventional dermal bandages include various types of adhesive plasters, adhesive tapes containing a drug for precutaneous administration, and the like. Wounds may be treated by applying gauze or absorptive cotton with, if necessary, a drug on the damaged part, and fixing it with adhesive tape. Further, a liquid bandage comprising a solution of polymeric material is also available, which is applied to the affected part with a spray or a brush, followed by removing the solvent by vaporization to provide a protective film on the affected part.
However, the treatment with gauze or absorptive cotton has a problem that the gauze or absorptive cotton adheres to the wound and, when removed, redamages the wound under recovery. The liquid bandage frequency causes pain upon application to the damaged skin due to the organic solvent used for dissolving the protective film-forming polymeric material. Moreover, it encounters a safety problem due to skin penetration of the organic solvent through the wound. Since cataplasms are composed of a paste of a water-soluble polymer with water and non-woven cloth or flannel as a support, they are not so irritative on the skin. However, they exhibit poor adhesion to the skin to give a feel foreign to the skin. The plasters or drug-containing adhesive tapes comprise a natural or synthetic rubber adhesive material containing a drug for percutaneous administration have recently been increasing in kind, but their direct use on the damaged skin has problems in that they not only exhibit strong adhesion but cause excessive maceration or dermatitis on the skin. In addition, since the adhesive tapes or the like should be applied to the dry skin as a prerequisite to their effect, they are hardly adhered to the skin wet with solutions, ointments, etc.
Therefore, it has long been demanded to develop dermal bandages which can satisfactorily be adhered to the damaged skin either directly or via drugs.
Water-soluble polymeric materials, such as polycarboxylic acids and anhydrides thereof, exhibit per se shape retention properties. They exhibit strong adhesion on absorbing a small amount of water, but absorption of excess water causes a reduction in viscosity and degradation to make a substantially dissolved state, thus resulting in loss of adhesiveness.
The inventors have extensively conducted a series of investigations in an attempt of improve the adhesion behavior of these water-soluble polymeric materials, i.e., loss of adhesion upon excessive water absorption, while retaining the strong adhesion observed when an appropriate amount of water is absorbed. To this effect, studies were directed to water-insolubilization of these water-soluble polymers. As a result, it has now been found that polycarboxylic acids or anhydrides thereof and vinyl acetate polymers have appropriate compatibility with each other and, when they are maintained in a compatible state or a nearly compatible state, substantial water-insolubilization of the polycarboxylic acids or anhydrides thereof can be achieved with their strong adhesiveness being retained or rather enhanced. It has been noted, therefore, that thin and soft films obtained from the compatible mixture of these two components do not undergo degradation due to water absorption in a wet state but exhibit long-lasting strong adhesion. The present invention has been completed based on this finding.